Regulation of hypoxic stress and oxidative stress in bone grafting: Current trends and future perspectives

Tissue engineering aims to offer large-scale replacement of damaged organs using implants with the com-bination of cells,growth factors and scaffolds.However,the intra/peri-implant region is exposed to se-vere hypoxic stress and oxidative stress during the early stage of implantation with bone graft materials,which endangers the survival,proliferation and differentiation of seed cells within the implants as well as the host cells surrounding the implants.If the bone graft material could spontaneously and intelligently regulate the hypoxic stress and oxidative stress to a moderate level,it will facilitate the vascularization of the implants and the rapid regeneration of the bone tissue.In this review,we will first introduce the signaling pathways of cellular response under hypoxic stress and oxidative stress,then present the clas-sical material designs and examples in response to hypoxic stress and oxidative stress.And finally,we will address the important role of epigenetic mechanisms in the regulation of hypoxic stress and oxida-tive stress and describe the potential applications and prospective smart bone graft materials based on novel epigenetic factors against hypoxic stress and oxidative stress in bone repair.The main content of this review is summarized in the following graphical abstract.

Function-oriented design:A novel strategy for advanced biomedical materials

It has always been a dream to construct tissues and even organs for transplantation to replace those with defects caused by diseases or injuries.Tissue engineering is another milestone in the developmental history of life science after cellular and molecular bioscience.Nevertheless,despite decades of rapid de-velopment,tissue-engineered biomaterials have not been widely used clinically.Biomaterials constructed by physical and chemical methods have lots of difficulty in precisely mimicking the macroscopic and mi-croscopic structures of human tissues.The ultimate way to build organoid tissue for regeneration is to enable the cells to take the initiative and build suitable functions.Based on the thoughts of tissue engi-neering,organoid technology holds great potential as a research tool for a wide range of fields,including developmental biology,disease pathology,cell biology,precision medicine,and drug toxicity and efficacy testing.This technology also holds tremendous potential for regenerative medicine,as organoids present the possibility for autologous and allogeneic cell therapy through the replacement of damaged or dis-eased tissues with organoid-propagated tissue or stem cell populations.In this review work,we briefly outlook the development history of organoid technology,summarize the current bottlenecks and the un-derlying reasons,and propose the unified term“function-oriented design in tissue engineering”,a new topic that may provide a solution to overcome these bottlenecks.

A single-cell transcriptome of mesenchymal stromal cells to fabricate bioactive hydroxyapatite materials for bone regeneration

The osteogenic microenvironment of bone-repairing materials plays a key role in accelerating bone regeneration but remains incompletely defined,which significantly limits the application of such bioactive materials.Here,the transcriptional landscapes of different osteogenic microenvironments,including three-dimensional(3D)hydroxyapatite(HA)scaffolds and osteogenic medium(OM),for mesenchymal stromal cells(MSCs)in vitro were mapped at single-cell resolution.Our findings suggested that an osteogenic process reminiscent of endochondral ossification occurred in HA scaffolds through sequential activation of osteogenic-related signaling pathways,along with inflammation and angiogenesis,but inhibition of adipogenesis and fibrosis.Moreover,we revealed the mechanism during OM-mediated osteogenesis involves the ZBTB16 and WNT signaling pathways.Heterogeneity of MSCs was also demonstrated.In vitro ossification of LRRC75A+MSCs was shown to have better utilization of WNT-related ossification process,and PCDH10+MSCs with superiority in hydroxyapatite-related osteogenic process.These findings provided further understanding of the cellular activity modulated by OM conditions and HA scaffolds,providing new insights for the improvement of osteogenic biomaterials.This atlas provides a blueprint for research on MSC heterogeneity and the osteogenic microenvironment of HA scaffolds and a database reference for the application of bioactive materials for bone regeneration.

Opposite Regulation of Chondrogenesis and Angiogenesis in Cartilage Repair ECM Materials under Hypoxia

Although cartilage tissue engineering has been developed for decades, it is still unclear whether angio- genesis was the accompaniment of chondrogenesis in cartilage regeneration. This study aimed to explore the process of anti-angiogenesis during cartilage regenerative progress in cartilage repair extracellular matrix （ECM） materials under Hypoxia. C3H10T1/2 cell line, seeded as pellet or in ECM materials, was added with chondrogenic medium or DMEM medium for 21 days under hypoxia or normoxia environment. Genes and miRNAs related with chondrogenesis and angiogenesis were detected by RT-qPCR technique on Days 7, 14, and 21. Dual-luciferase report system was used to explore the regulating roles of miRNAs on angiogenesis. Results showed that the chondrogenic medium promotes chondrogenesis both in pellet and ECM materials culture. HIF1α was up-regulated under hypoxia compared with normoxia （P 〈 0.05）. Meanwhile, hypoxia enhanced chondrogenesis, miR-140-Sp exhibited higher expression while miR-146b exhibited lower expression. The chondrogenic phenotype was more stabilized in the ECM materials in chondrogenic medium than DMEM medium, with lower VEGFα expression even under hypoxia. Dual-luciferase report assays demonstrated that miR-140-5p directly targets VEGFct by binding its 3＇- UTR. Taken together, chondrogenic cytokines, ECM materials and hypoxia synergistically promoted chondrogenesis and inhibited angiogenesis, miR-140-5p olaved an imnortant role in this process.

Bioadaptive Nanorod Topography of Titanium Surface to Control Cell Behaviors and Osteogenic Differentiation of Preosteoblast Cells

Titanium （Ti） nanorods fabricated using selective corrosion of Ti substrate by anodic technology show better biocompatibility with pre-osteoblast cells. The current study investigated the response of the murine pre-osteoblast cell MCST3-E1 on Ti nanorod topography and untreated Ti surfaces by means of examination of the morphology and osteogenic differentiation responsible for the pre-osteoblast reaction. The morphology of MCST3-E1 cells was observed using scanning electron microscopy, and alkaline phosphatase （ALP） activity was measured using a colorimetric assay after incubation for 7, 14, and 21 days. The expression of three osteogenic differentiation markers including ALP, osteocalcin （OCN）, and collagen type 1A1 （COL1A1） and two transcription factors including runt related transcription factor 2 （Runx2） and osterix （Osx） at different time points was detected using real-time polymerase chain reaction analysis in both groups. Osx was used to confirm the protein level. The results showed that Ti nanorod surfaces provided prolonged higher levels of ALP activity compared with unmodified Ti surface on the 14th and 21st days. Gene expression analysis of ALP, OCN, and COL1A1 showed significant upregulation with modified nanorod topography after incubation for 14 and 21 days. Osteogenic transcription factors of Runx2 and Osx exhibited changes consistent with the osteogenic differentiation markers, and this may contribute to the persistently active differentiation of MC3T3-E1 cells in the Ti nanorod group. These results demonstrated that the current nanostructured surface may be considered bioadaptive topography to control cellular behaviors and osteoblast differentiation. The in vivo performance and applicability are further required to investigate osseointegration between implant and host bone in the early stages for prevention of aseptic implant loosening.

Biosynthesis of Bioadaptive Materials:A Review on Developing Materials Available for Tissue Adaptation

Biomaterials are increasingly being evolved to actively adapt to the desired microenvironments so as to introduce tissue integration, reconstruct stability, promote regeneration, and avoid immune rejection. The complexity of its mechanisms poses great challenge to current biomimetic synthetic materials. Although still at initial stage, harnessing cells, tissues, or even entire body to synthesize bioadaptive materials is introducing a promising future.